Life cycle:Stoneflies undergo incomplete metamorphosis. Their life cycle includes three stages – egg, nymph and adult. Many species produce one generation per year, but some species require up to 3 years to an adult capable of reproduction.

Introduction:
Stoneflies are old order of insects undergoing incomplete metamorphosis. In body shape, aquatic nymphs resemble their terrestrial adults.

Stoneflies are generally sensitive to pollution and are among the most sensitive orders of aquatic insects. Many species are restricted to habitats with high levels of dissolved oxygen, making them an important water quality indicator (large number indicates good water quality).

Some species of stonefly nymphs, living in highly oxygenated water, may not have gills and rely on oxygen diffused only through the skin.

Other species have developed gills, in order to increase the body surface and overall breathing efficiency. Gills are formed in tufts of fine filaments which are sometimes visible around the base of legs, bottom of the thorax or on the tip of abdomen.

Nymphs of some species can be mistaken for mayflies, but following characteristics distinguish stoneflies:

– Presence of two claws at the end of each segmented leg / mayflies have a single claw.

– Two pairs of wing pads (barely visible in young instars) / mayflies have one pair.

– Most of the stoneflies do not have gills on abdominal segments / mayflies do.

Shape and position of wing pads, caudal filaments, gills and shape of the mouthparts are used to distinguish among the stonefly species.

To emerge, nymphs crawl out of the water and secure their tarsal claws in some solid surface. Nymphal skin splits on the head and thorax and adult stonefly climbs out. In comparison with the nymphal stage, which can take up to three years, an adult stage is very short and takes up to one month. Adults feed on nectar, algae and lichens that grow by the water.

Stonefly nymphs (Plecoptera):

Alderfly larvae
(order Megaloptera, family Sialidae)

Feeding:
Predators actively searching the bottom for some smaller animals.

Habitat:Alderfly larvae inhabit still waters and slow flowing sections of streams and rivers.

Movement:Larvae burrow in fine sediments at the bottom.

Size:Mature larvae grow up to sizes around 30 mm.

Life cycle:Alderflies undergo complete metamorphosis. Their life cycle includes four stages – egg, larva, pupa and adult. Fully grown larvae crawl out of the water and dig a cellar in damp soil to pupate. Alderflies require 1 or 2 years to an adult capable of reproduction.

Other characteristics:elongated and flattened body; head and thoracic segments sclerotized; abdomen soft without hardened plates; pairs of tapering filaments on the sides of abdomen; each segmented leg ends with two tarsal claws; single caudal filament with rows of short setae

Alderfly larvae (Sialis lutaria):

Spongillafly larvae (order Neuroptera, family Sisyridae)

Feeding:
Piercers using their long and curved (stylet-like) mouthparts to pierce the cells or freshwater sponges and suck the fluids.

Habitat:Spongillafly larvae inhabit both running and still waters where freshwater sponges are found.

Movement:Larvae crawl on the surface or in the canals of freshwater sponges.

Size:Mature larvae grow up to sizes around 5 mm.

Life cycle:Spongillaflies undergo complete metamorphosis. Their life cycle includes four stages – egg, larva, pupa and adult. Eggs are laid by adult females on the overhanging vegetation. When the larvae hatch from eggs, they fall into the water and search for the sponges. They remain close by all the larval stage. When the larva is fully grown, it leaves the water to spin a cocoon and pupate.

Other characteristics:
Greenish or yellowish colour of spongillafly larvae matches with the sponge. Long segmented antennae are slightly longer than the piercing (stylet-like) mouthparts. Each leg bears a single tarsal claw. One pair of hardened plates is located on the top of thoracic and abdominal segments. Stubby body is covered with long setae.